Blanket recommendations dominate the advisory landscape for African smallholder producers, yet their farming conditions, investment capacities, and production orien- tations are highly diverse. Current, field-specific (4R) nutrient management advisory neglects that fertilizer costs pose a binding constraint. African smallholders’ actual fer- tilizer use is highly variable, as is the efficiency of its use. To achieve higher nutrient use efficiency, fertilization needs to match other agronomic management practices, such as land preparation, crop rotations, weeding, timing of operations, manure use, etc. Premised on the idea that such (past) agronomic management shapes soil fertility and is key to improving productivity, resource use efficiency and to lowering GHG emissions, our research in Tanzania uses a customizable mobile phone application to: (1) assist farmers in building a field-level administration of their agronomic management prac- tices; (2) instantly use this data to provide tailored, Management-Based-Advice (MBA) for individual fields, and; (3) fill a key agricultural data gap – e.g. longitudinal, field-level management data that can inform future advisory. In the first two seasons of use, more than 1,000 field-specific advices were provided by some 40 extension workers, ena- bling farmers to use their available resources – labour, manure and purchased fertiliser, more efficiently and cost-effectively.